GPR Survey to localize and analyze Tombs beneath the paving of Modern and Medieval Churches. A Case of Study from the Cathedral of Padova (It)

Guglielmo STRAPAZZON | Rita DEIANA
(Department of Cultural Heritage, University of Padova, Italy)

Keywords: GPR, graves, Medieval Churches, GIS, 3D

Abstract:
Graves are one of the most common archaeological features present beneath modern and medieval churches. Graves are frequently hidden by later paving, so their position and their structure are mostly unknown to archaeologists. Furthermore, archaeological excavation are usually not possible or have limited extension in religious building that are still in use, making this method unable of obtain a complete understanding of the mortuary landscape hidden beneath the actual paving.
Ground Penetrating Radar can help to provide such information without any invasive operation, allowing both an extensive mapping of the churches subsoil, and giving useful information about the structure of build tombs.
Between 2012 and 2014 several GPR surveys took place inside the actual Cathedral of Padova (built between XVI and XVIII centuries), following two different strategies of data collection and analysis. First an extensive survey with broader profile spacing and lower antennas frequencies (ranging from 200MHZ to 600MHz) provided an extensive map of the subsoil of the church. The collected geophysical data were inserted in a GIS environment, among with historical maps that depicts some portion of the demolished romanesque phase of the older cathedral (that was previously built on the site) and some of the tombs positioned on its naves. New graves were identified.
Later 4 of the 71 tombs previously detected by the first geophysical prospection were investigated with a high resolution GPR survey (with a 900MHz antenna). A tridimensional model of the isosurfaces of the amplitude of the recorded GPR signal were realized in order to analyze the structure of the selected tombs.
The research shows how different GPR survey strategies, integrated with the analyses in GIS environment and the creation of 3D model of the data, allow a better comprehension of the subsurface that lies beneath modern and medieval churches.